Physics Based Critique of the Petrov Method

[PVstudent]

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[PVstudent]

Just as a point of reference. This is the 8th grade boy I am working with...and this plant makes me giddy! Really, I've only had about 4 sessions with him (he had to sit out the beginning of the season with a foot injury). I also have a 9th grader who has gone from 8' last year to 10' 6" already this year and who is just beginning to have a swing. By next year I'm hoping to have 3 boys and at least 2 girls, 4 of which will be either 9th or 10th graders at the 2A MO state meet...

Firstly great job with this novice.
Secondly from Owen's body posture, depicted in the photo, the orientation and spatial organisation of the limbs and torso is excellent for someone who is just learning to swing.

Given that his take-off is very close to the planting box are you encouraging this young lad to bend the pole at this stage in his development? Have you dismissed the notion that learning to swing following the take-off is easier to teach on a stiff pole? From my experience I have found this to be the better option in terms of long term results. I am very interested to hear what you have to say in this regard.

Bearing in mind the limitations of a single photo, I raise with you the question of how effective you found Owen's penetration towards the landing pads to be? The photo gives the impression that he has "force bent the pole via the stiffened lower arm" and consequently is momentarily stuck in his take-off body shape before he can actively engage swing leg? Is this the case or was Owen swinging relatively freely and penetrating effectively toward the centre of the landing pads.

Great to see what the coach and vaulter actually can do in real world action.

Good stuff, but check out what the lower arm is doing and if that is what you want to be happening.

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[willrieffer]

Will many thanks for your considered response to my last post. I have prepared some diagrams to try to clarify, for myself and possibly others, what you are meaning specifically when you discuss the changing role of gravity in relation to the action of the lower arm in particular that you believe is not considered in the PB methodology.

First, I DO think that the PB model is effective in this regard. They were highly interested in hip/CoM placement in the early vault and almost all of their methodology in that regards, their concern that the hips not be thrown forward by such effects as pole braking, work in this regard. They keep the hips back initially, re-align back while often "filling" with the left, and also work toward and carry a lot of radial energy in the take off foot and lower leg while also slowing the hips. Much of my ideas actually came from slo-mo viewings of Bubka!

I still do not agree that I have taken liberties with the energy exchange graph. Nor do I accept your argument that there is not a differential increase in the total energy of the vaulter that can be attributed to vaulter's work in the pole bending and recoiling phases.

Ok. Let my try another tack. There are two types of high bar drills we might consider. Swing drills and Bubka's. Swing drills are relatively "flat" or are tied to the horizontal. Bubka's are tied to the vertical and are primarily concerned with "lifting" the vaulters CoM. For this specifically one needs something to pull/push on which in the case of a vault is the pole decompressing to vertical. Their relationship to potential energy are far different. One can enact a swing from a run onto the high bar passively. In fact I do this drill with my vaulters and so the vaulters swing again has elements of its energy come out of the effect of the take off effects, i.e. running momentum and pole braking, again something Petrov was keenly aware of in regard to our concerns here. We also know that some advocate for a more "passive" or natural swing while again we want to recognize Petrov's focus on it in the early swing and being "active" toward it.

The swing phase is very complicated, we know this. What is apparent however is that it has a tolerable window for the vaulter to hold their CoM in during the swings progress in time. If the vaulter "pushes" their CoM outside of this window, the vault fails. This happens all the time with beginning vaulters. They pull up on the pole early and as an example while this increases both their work they are doing and immediately increases their potential energy, it also stops a good vault from happening. Why? Because they have by work pushed their CoM out of the tolerable window set by the relation of the vaulters CoM, the pole, and gravity. Most notably in losing their relationship between gravity and the bending pole they have lost the resolution of the gravity vector into the pole compression rate. This happens as well when any vaulter take off "under" in the normal sense. Their swing CoM leaves the window for a good vault by being progressed which again puts the vaulter in a position where gravity adds less to pole compression while also draining more energy from the swing. Think about it. Think about a person on a normal backyard swing. The farther forward they swing, the more they slow down, and the more gravity is pulling them back toward earth. Of course this is the source of potential energy, but it is also everything a vaulter is fighting against! One of the other effects that can be seen in this common backyard swing system is "flying". The swinger "flies" when the forces of centripetal acceleration and gravity reach zero against their chains and they rebound into a moment of free fall. This only happens when the swinger slows near the top of the swing and when gravity is pulling perpendicular to their chains. If one "catches" a swinger only part way through their swing, they will not "fly" as gravity will still pull them down into the seat as well as along the chains. These are the effects I'm concerned with an I hope now you can see why. But these relations are terribly terribly complicated in a vault. The vaulter generates compression in the pole by means of several forces. Take off velocity and vector. Centripetal acceleration of the swing which is probably maximized when they cross the chord. And finally by the gravity vector being resolved and added to compression. And, while the vault is going on ALL of these values are changing! Its a mathematical nightmare involving a system of differential equations!

Also I do not yet understand how an inanimate object such as a vaulting pole can be bent vastly beyond the range of deflection due to that induced by pole weight force and the moment it produces without an external agent producing that deflection increase. The external agent has got to be the vaulter! The other factors influencing the pole bend are trivial in comparison and on this we agree.

The agent IS the vaulter, but the force of gravity never ceases to act on the vaulter during the vault. Therefore it cannot be left out of any energy consideration including pole compression. Gravity does work, through the vaulter on pole compression and must be considered at all times in the energy relation. In the same way vaulting has changed from straight poles to flexible ones think of the difference between spring board diving and platform diving. IN both diving forms divers routinely do jumps and pre-jumps. If we consider the divers bodies as being equally capable of energy generation in both forms, we then consider the results where springboard divers are returned greater heights and far more potential energy capacity. Why? The flexible nature of the board with the effect of gravity grants greater acceleration through decompression! The pole vault is similar...and also different in that its much more complicated!

Also how do you account for the kinetic energy decrease of the vaulter followed by the increase in kinetic energy? The energy has to have gone somewhere and some of it regained by the vaulter during initial pole recoil. The vaulter has more energy at pole release than at take-off. How do you account for this? How did the pole bend if not from the vaulter exchanging energy with it. The vaulter's weight obviously has a contribution as does his muscular useful work on the pole.
I think we will have to agree to disagree here and move on.

I don't think we have to disagree, although I'm not sure what is in contention! It's a complicated movement with varying rates of speed. The whole act of the vault is to redirect energy from the horizontal to the vertical. In this I find it no surprise that the vaulter first slows and then speeds up on a first compressing and then decompressing pole. The rates of all of these movements are very very important. A slight change in rate in pole compression or swing moment will doom a vault!

Vaulters do add to the energy. Have to. Must be so! A "Bubka" on a high bar radically alters a vaulters relation to gravity and thus potential energy.

The simplification in the diagrams is deliberate and is done to try to be obvious. I am happy and aware that in this case I am taking liberties in regard to the actual complexity of the situation described.

You've looked at the diagrams right! Really, you are 100% correct and I still have humor tears in my eyes!

That's a lot of work, sir. A lot. Thank you. I know I did not address them specifically. Just there is ALWAYS a gravity vector addition to the vault. It has to be resolved with a vector diagram (which I must admit I have not done in....decades) into its pole compression (and decompression) element versus its swing slowing element...which is changing all the time!

Look, let me try and get to the basic idea I've put forth before. In looking at a lot of beginning vaulters enact bad vaults I just started to notice things based on my physics schooling. They usually go out of the CoM "window" by either going above it, i.e. they pull on the pole, or in front of it, i.e. taking of under and/or "hugging" the pole. Both things make them what I call "swing progressed" where gravity now is not adding at a high enough rate to pole compression while also draining at a faster rate from swing momentum. The vault is doomed. If that is the case, then should we not look at the opposite as being beneficial to the vault? That is would not advanced vaulters want to push the envelope toward the lowest and furthest back area of the window where they can still enact the vault? I think so. How is that accomplished? Well, they simply have to press back and down early on and try and retard the swing as much as possible while still enacting the vault. If you go back and watch the evolution of the vault you will see this effect take place! While not saying so specifically, the Petrovian's were aware of this relationship, and acted on it in their approach to the take off and early swing. Moving the take off back can and often does have a positive effect on this relationship. I watch Bubka and he is a master of reorienting back (a retardation of the CoMs forward motion that, yes, generates energy in the system and in the pole), keeping the hips quiet and smooth while all the while generating and carrying a high amount of radial energy in his take off foot and leg throughout the swing as is necessary if you are at all going to retard the CoM in the swing. These vaulters store more energy in the pole and swing extremities only to reclaim it later.

That's it. This is not old school american max pole bend OR free swing stuff. Its an orientation to gravity methodology that in fact owes a lot to Petrov's ideas and is in many ways I think, an extension of them, not in the particular, but in the general. It owes its generation to what causes bad vaults more than to what has seemed to create good ones, and a lot of thought experiments in physics. I hope that helps.

[willrieffer]

Diagrams and Vectors

Uh, wow. Let me see if I can explain. And again, I have not done this in....decades.

The gravity vector has to be resolved into components and added or subtracted to the other forces. The easiest one is swing momentum. We know swing has a vector perpendicular to the swing chord so it points up at an angle. You have to resolve the vertical element of the swing moment (it has horizontal AND vertical elements to the frame of reference, namely again set by gravity} with gravity, which is to say, gravity is slowing it down. What is left has to be resolved into the CoM, and has an angular component through the body and more or less to the top hand. Part of that is then resolved into pole compression. Do not forget that the pole is pushing both BACK and UP on the vaulter in its own component forces. As its upward element is carrying the vaulter upward (they all go up continuously) we can set the rest of the gravity vector against this. The outcome is it effects both the rates for the potential energy curve and the pole compression.

Then there is also the centripetal force of the swinging vaulter...

It's, uh, very complicated and changing all the time throughout the vault.

Like I said, the easiest thing to do here is imagine a vaulter who has somehow found himself far swing progressed so that he's parallel to the ground. Now the gravity vector is resolved completely into slowing the swing and not at all into pole compression.

I hope that helps.

What can be stated is that the less gravity has to be resolved into swing deceleration, the more it can possibly add to compression.

[willrieffer]

Firstly great job with this novice.
Secondly from Owen's body posture, depicted in the photo, the orientation and spatial organisation of the limbs and torso is excellent for someone who is just learning to swing.

Given that his take-off is very close to the planting box are you encouraging this young lad to bend the pole at this stage in his development? Have you dismissed the notion that learning to swing following the take-off is easier to teach on a stiff pole? From my experience I have found this to be the better option in terms of long term results. I am very interested to hear what you have to say in this regard.

Bearing in mind the limitations of a single photo, I raise with you the question of how effective you found Owen's penetration towards the landing pads to be? The photo gives the impression that he has "force bent the pole via the stiffened lower arm" and consequently is momentarily stuck in his take-off body shape before he can actively engage swing leg? Is this the case or was Owen swinging relatively freely and penetrating effectively toward the centre of the landing pads.

Great to see what the coach and vaulter actually can do in real world action.

This group effectively had little coaching last year. The HC is actually a great coach, but like many, spread far too thin to do much with the vault. SO he recruited me...

We had to start from the beginning with pole grip and carry, run consistency, etc. We do stiff pole sand box drills and also short run stiff poles. Then there is the period of finding longer run lengths and approach adjustment. Then its a lot of back and forth trying to get a proper plant for the full approach as beginners tend to digress from the elements time and again. And so we progress and digress over the drills much over time. There are continual concessions made....

To answer one question first, he's landing too deep actually, and that's the last he's going to see of that pole. And that's with a relatively poor swing extension. And he was probably a tad under in the vault in the pic. He more or less passed that pole in a day.

He's the only one that has that left arm of my whole bunch and where the rest of them have a tendency to "leap" into the pole and where head closes with the pole and the left elbow actually passes the pole. So for them I have to encourage them to press up with both hands into the vault and keep the pole "ahead" of them. He, of course, took this to heart, and it is problematic in many ways. For one, there is really not time on this scale to enact this sort of vault. The poles are too short, the available swing time too short, etc. And he was blocking very badly. Left arm action is very...contentious. For these kids there is the need for "space" from the pole, to get them back some and not leap into it, and yet there is little to no time or the arm is blocking. Like I say, when I get back to him and work stiff pole swing drills (we also do bar swing drills), he'll probably lose that arm action inadvertently but almost necessarily.

Most of the gains have come from simply working out approach and plant mechanics, i.e. they are not "under" all the time and enact many more fully extended plants. I have one kid who is a more natural swinger than anyone I've ever worked with and its with him I expect the biggest end gains in this season. He currently does a very good stiff pole swing to invert, but cannot re-enact it on a full run and bending pole.

For not spending more than about 4-6 hours with him, I'm very excited.

[altius]

willreifer old son I apologise for questioning you. I bow to your infinitely greater wisdom and experience - and probably your success as a coach. I can see that I have nothing to offer you in any of those areas so I will stop trying. However I would suggest, with great humility of course, that you read my book on the Petrov/Bubka method and appreciate the way the ideas in it can be applied to teaching and coaching young athletes. This will save me a great deal of embarrassment as you publicly rebut anything I post on PVP.

However in my defence I would point out, with great humility of course, that for a period of around thirty years I was as successful as anyone at taking beginners and helping them become technically sound pole vaulters who have achieved satisfactory results. This in the track and field wilderness of Adelaide. You will find an outline of some of those performances in Chapter Eight I believe.

PVstudent is younger and more resilient than I am, so I hope he will continue to try to educate the doubters. I can only wish him good luck.

But just a thought -could you detail how the technical model you are teaching the lad who has jumped 10'8"?? will allow him to progress - say to 16/17/18' - without any major modifications. I have just started coaching individual athletes again after a nine year break and I may be a bit out of date - so I would welcome any advice on how to proceed. Thanks in anticipation.

[PVstudent]

Just to help readers view the performances and the biomechanics analysis of Bubka's 1987 performances at the IAAF 2nd World Championships in Rome please review this utube video.

http://youtu.be/7j6al8B_ANg

Will, hope you find this informative. I will respond in due course to your and other discussants responses to the Statics analysis and simple model of the vaulter pole vertical force interaction. Similarly I hope there will be some comment on the importance of shape and advantages the curvilinear pathway gives to modern pole vaulters. I understand that ploting this pathway may involve differential and integral calculus.

But by simply ploting the vaulter's COM for every fame/video field and just joining the successive x,y coordinates of the COM gives a pretty good estimate of the curvilinear pathway.

(For this to be accurate the original footage must be from spatially and time calibrated cameras preferably located orthogonal to primary plane of vaulter motion of interest. Panning requires special algorithms to be used in correcting the spatial co-ordinates which were used by the investigators.)

Enjoy the video which has been edited from the original film.

It does highlight some of the post take-off Petrov-Bubka characteristics!

[willrieffer]

willreifer old son I apologise for questioning you. I bow to your infinitely greater wisdom and experience - and probably your success as a coach. I can see that I have nothing to offer you in any of those areas so I will stop trying. However I would suggest, with great humility of course, that you read my book on the Petrov/Bubka method and appreciate the way the ideas in it can be applied to teaching and coaching young athletes. This will save me a great deal of embarrassment as you publicly rebut anything I post on PVP.

However in my defence I would point out, with great humility of course, that for a period of around thirty years I was as successful as anyone at taking beginners and helping them become technically sound pole vaulters who have achieved satisfactory results. This in the track and field wilderness of Adelaide. You will find an outline of some of those performances in Chapter Eight I believe.

PVstudent is younger and more resilient than I am, so I hope he will continue to try to educate the doubters. I can only wish him good luck.

But just a thought -could you detail how the technical model you are teaching the lad who has jumped 10'8"?? will allow him to progress - say to 16/17/18' - without any major modifications. I have just started coaching individual athletes again after a nine year break and I may be a bit out of date - so I would welcome any advice on how to proceed. Thanks in anticipation.

And possibly you might wonder why you don't have more adherents...

I'm trying to teach them a Petrovian free take off, but without strapping rockets to their buttocks I doubt any of them have the natural speed to reach anywhere near those heights. With good form its more like 12' - 15' for the boys and 8' - 11' for the girls. I expect I'm worth about 2' to 3' to them in their career over not having any coach at all. That many more of them will visit the State track meet, and the perhaps a couple of them will vault for minor colleges.

But, hey, good luck. Hope your model isn't dying....

[willrieffer]

Just to help readers view the performances and the biomechanics analysis of Bubka's 1987 performances at the IAAF 2nd World Championships in Rome please review this utube video.

http://youtu.be/7j6al8B_ANg

Will, hope you find this informative. I will respond in due course to your and other discussants responses to the Statics analysis and simple model of the vaulter pole vertical force interaction. Similarly I hope their will be some comment on the importance of shape and advantages the curvilinear pathway gives to modern pole vaulters. I understand that ploting this pathway may involve differential and integral calculus.

But by simply ploting the vaulter's COM for every fame/video field and just joining the successive x,y coordinates of the COM gives a pretty good estimate of the curvilinear pathway.

(For this to be accurate the original footage must be from spatially and time calibrated cameras preferably located orthogonal to primary plane of vaulter motion of interest. Panning requires special algorithms to be used in correcting the spatial co-ordinates which were used by the investigators.)

Enjoy the video which has been edited from the original film.

It does highlight some of the post take-off Petrov-Bubka characteristics!

Well, I watched it once so far. It will take repeated viewings as it progresses rather rapidly to....well, think about physics.

1) The curve for vaulter success as they present it generally follows the curve for vaulter take off speed sans Vigneron. This might make him the outlier worthy of interest as he seems to have accomplished greater heights despite less take off velocity and approach deceleration*. It also points again to the idea that take off KE = 1/2m(v squared) is a highly dominant consideration in vault analysis and mechanics. Or, that the gains inside the vault can be dominated by sheer differences in take off velocity. Like I say, the most interesting vaulters should be the slowest ones to vault high heights. Even within the Petrov system this would indicate toward an analysis of Tradenkov in contrast to Bubka.

2)It lacks any interest in gravity, its effect on swing moment or pole compression outside of the measurements given. They may be in some ways insightful on the topic as the rates of many motions are recorded, but as to whether or not results can be derived, at this point I cannot say.

*The method of the PB model in its approach to the runway and take off approach should be of great interest as it notes the Russians were accelerating into the take off at higher rates and to higher take off velocities than the other vaulters in general.

[vquestpvc]

Just want to thank Kirk for his link to the "Round Table with Sergery Bubka". Having read this info numerous times as second hand information, it was good to get something direct from the "horse's mouth". I feel so on the right track concerning what I'm teaching and why right down to what Bubka stated in the point of focus stating "the box doesn't move". Further thou, perhaps Bubka didn't always accomplish a free take off, but he always attempted it. Being on a 17' pole makes it a little more difficult than a 12'-13' pole. However, I believe it is important to teach young vaulters this concept as it leads to jumping at take off. Regarding Bubka's overall technique, I don't believe the current world record holder, Lavillenie, will ever have as many big jumps as Bubka because of the varying technique.

[KirkB]

Another interesting quote from Bubka (and one of my favorite topics!) in that same article:

Q. How would you describe the action of bending the pole?
A. Before the fiber glass pole, pole vaulters put their focus on moving the pole, then, when the flexible pole appeared many people put their focus on bending the pole. The pole bends as a result of the speed and mass of the jumper, therefore, it is more important to concentrate more on moving the pole towards the plane of the bar, rather than being aware of bending it. If the vaulter can put all his speed to the pole, the bending of the pole will happen in a very natural way and this, together with a good height of grip will ensure good results.

I have bolded and underlined the main points.

Kirk

[willrieffer]

Two years ago I probably had the fastest kid I've ever had in the vault, and for a month he straight poled the vault at full speed from a full run. Or, you can put a lot of speed and jump into a vault in such a way that it will not put the necessary force relation on the pole to initiate and carry a bend. Then one day he finally pushed the plant up and forward which also kept his hips back and down and the pole bent and soon we had to move him off this pole. I had this happen again this year with a female vaulter. Take off speed alone will not necessarily bend a pole, but it comes from a relationship of the vaulter to the pole at speed AND gravity. Like I said, if some of these ideas floating around actually held, we could go back to the old slide the bottom had up form of straight pole vaulting. But no one is doing that, why? Because you need two hands spread on the pole and some intent and technique to initiate a pole bend. Also, that the front hand is a necessary anchor point to control the swing position and rate.

Bubka should have more height clearances than Lavillenie because he was faster and taller. Again, if you consider take off energy being dominated by take off velocity squared its easy to see why this should be and why in the IAAF video clearance height follows a curve aligned with take off velocity. Bubka had the fastest take off velocity and had cleared the greatest height. What does this say? Well, in one sense it might well say that minutia of swing mechanics are overblown. That is as long as a vaulter can, by whatever means, keep their CoM inside the tolerable window, take off speed will carry them to height. This is why Dosevi can make a safe clearance of 5.75 off of a radical under step by locking his hips back against pole braking and thus keeping himself in the CoM window. How this is done is of little consequence to physics (again notably the dominance of velocity squared in KE = 1/2 M {Velocity squared}) whether its by a free take off or by a locked left and double leg swing.

Also, while Bubka has the greatest take off velocity and height in the IAAF video, VIgneron places second with a take off velocity under the curve. This would point to the idea that his efforts from take off to clearance inside the swing are possibly MORE efficient that Bubka's. Somewhat counter-intuitively, Bubka's great take off speed and energy should allow him to overcome certain elements of swing inefficiency where they exist.* And why we consistently see the French contingent over time show world class heights from smaller and slower athletes, i.e. they actually have the most efficient swings in relation to gravity. This is simple logic and physics. Slower take off speeds and high heights can ONLY come out of higher swing efficiency.

These guys said a lot of things. A lot of PV coaches say a lot of things about "physics" that have very little real relation to the realities of physics. Somewhere on here we have Altius saying Bubka told him there were better athletes in his time in the PV. Okay, he can say that, but when we look at the fact that he consistently showed greater take off velocity than most other vaulters in history, and certainly as measured in the IAAF video, and we know the relation of velocity to energy, we can see that these claims should not be taken as physical claims, but as psychological ones.

As I progress through the video again, we again see the claims that work inside the vault leans on a biomechanical generative idea associated with the swing, and does not address the gravity relation at all. The IAAF video makes a claim that the max potential energy position over take off energy comes from Bubka's work inside the swing and disregards the work done by gravity acting though Bubka on the compressing pole and any sort of efficiency ratio in this regard. This is where the study falls short and leads to both an obvious claim, that Bubka's vault is efficient, and leads to a dubious conclusion that this is resultant from singularly his biomechanical generation of energy sans his relationship to gravity. My conclusion is that he was probably both gravity efficient in the compression phase, AND biomechanically efficient in the decompression phase. How much so this is the case, or if in fact it is the case, over other vaulters, especially ones with lower take off speeds remains unanswered.

The study of pole speed and swing velocity is interesting. I might say it shows that by his greater take off speed he is allowed to progress faster in his swing than other vaulters. OR, gravity forces them to stay back in the swing for longer, which accounts for the pole speed slowing effect. Bubka, because he takes off with such speed, can find an allowance to keep a higher angular swing velocity and rotate into the negative. This is a trade off. As I have described, Lavillenie is going to have a much different swing rate, slower, as the video proposes for other vaulters in it, yet he is going to show a radical shift in his "tuck" phase, where after slowing his rotational velocity is going to "jump" has he tuck speeds to the vertical. I believe that even within the Petrov system Tradenkov made this sort of swing speed adjustment, which I claim is necessary for slower vaulters to achieve 6m plus heights.

*This is a contentious and difficult to prove point as we have to resolve clearance versus actual vaulter height as max potential energy and where Bubka was often noted for huge clearances over the bar. And so while its contentious to propose that Vigneron is more efficient than Bubka, its probably more likely that he was more efficient than Gataulin, whom I will guess was a Petrov vaulter, as the video shows that Vigneron clears a greater height with less take off velocity.